Hot melt thermoplastic adhesives have been widely used in industry for adhering many types of products, and are particularly useful in applications where quick setting time is advantageous. One application for hot melt adhesives which has been of considerable interest in recent years is in the cartoning and packaging industry. Hot melt adhesive beads are extruded through nozzles onto the major and/or minor flaps of a carton or package traveling at a high rate of speed, and then the flaps are subsequently folded together to effect a bond therebetween. A wide variety of packages and cartons are formed in this manner, including those requiring a "sift-proof" seal between the flaps, i.e., one in which all leakage paths through the flap connections are eliminated.
In order to ensure that the flaps of a carton are securely bonded to one another, it is desirable to apply an adhesive pattern consisting of extruded beads which extend transversely or at right angles to one another on the major and minor flaps of the cartons. This involves the application of one or more extruded beads onto a major or minor flap in the direction of movement of the carton or package, and at least one extruded bead along the flaps in a direction transverse, i.e., perpendicular or angulated, with respect to the direction of the substrate movement. In many cartoning or packaging applications it is necessary to deposit either a continuous bead, or a number of laterally spaced beads, across substantially the entire width of the flaps which are transverse to the direction of movement of the carton to obtain the desired bond.
One structure which has been employed in cartoning and packaging applications to apply a number of laterally spaced beads to the transverse flaps of a carton is a "T-bar" nozzle such as disclosed, for example, in U.S. Pat. No. 4,659,016 to Faulkner. The T-bar nozzle disclosed in the Faulkner U.S. Pat. No. 4,659,016, and other nozzles of this type, comprises a rectangular-shaped nozzle body or bar formed with an inlet, an internal distribution passageway and a number of spaced outlets or orifices each supporting a discharge nozzle. The nozzle body is mounted to the housing of an adhesive dispenser such that hot melt adhesive is ejected from the dispenser into the inlet of the nozzle body and transmitted through its internal distribution passageway to each of the outlets. These outlets direct the hot melt adhesive into the discharge nozzles, each of which extrude a separate adhesive bead for deposition onto a substrate. In a cartoning application, a T-bar nozzle of this type can be positioned with respect to a transverse flap of the moving carton so that it dispenses a number of extruded beads which are laterally spaced along substantially the entire width of such transverse flap.
While the construction of T-bar nozzles of the type described above lends itself to the formation of cartons and packages, a number of problems have been encountered with their use in such application. One problem involves imprecise cut-off of the adhesive flow through the nozzle which produces undesired drooling or stringing of the adhesive onto the nozzle and/or substrate. It can be appreciated that the T-bar nozzle must be operated intermittently as the flaps of individual cartons are moved therepast at relatively high line speeds. It is believed that a relatively high amount of adhesive is allowed to pool within the inlet, distribution passageway and outlets of the rectangular nozzle body of T-bar nozzles such as disclosed in the Faulkner U.S. Pat. No. 4,659,016, and this excess adhesive escapes or drools from the discharge outlets of the T-bar nozzle when the flow of adhesive from the dispensing device into the nozzle inlet is intermittently interrupted or cut off during a production run.
Another cause of drooling or stringing of adhesive from T-bar nozzles is that a relatively high temperature differential is created between the adhesive ejected from the dispensing device into the inlet of the nozzle and the adhesive which is ejected from the discharge outlets thereof. In the T-bar nozzle disclosed in U.S. Pat. No. 4,659,016, for example, a temperature drop of from about 20.degree. to 90.degree. F. can be created between the adhesive in the dispensing device and the adhesive which is ejected from its discharge orifices or outlets. This substantial temperature differential is undesirable because it permits stringing or drooling of the adhesive, i.e., the discharge of thin adhesive strands or "angel hair" from the outlets of the T-bar nozzle. The formation of adhesive strands can result in a glue build-up on the packaging machine, thus requiring a shut down of the packaging or cartoning line for cleaning and maintenance.